so im desining my engine for the datsun 510 (gotta putt it on paper first) and it all came down to a 13b 4-port bridgeported with adi 51 carbs (target is for about 240hp) , i was wondering for the rotors if it is better to use rx8 rotors (10:1 compression) or are there other rotors that are hihger compression?

 

the rx8 rotors are the highest, check out some of the other threads that have been written and what people ahve to be able to do, possibly an easier alternative would be to get a good used set of s5 NA rotors, those are out of the 89-91 non turbo 7's they are almost as light and still pretty high compression.

CJG

 

can i use carbon apex seals with that high a compression ratio?

 

Discussion for Retrofitting Rx-8 Rotors, and yes, carbon seals should be used with a N/A bridgey.

 

ieither way you go (s5 or renesis) you need the whole rotating assembly since the shafts and counterweights all go together.

id spring for the renesis rotors tho, a good amount lighter than the s5 n/a and belive it or not, cheaper as a new oem part. an entire new renesis rotating assembly would probobly run you about $2000-2500 or maybe less including the price to mill out the apex slots.

new parts, especialy those alredy designed for 9000rpm stock (the renesis assembly), are going to be ideal (both for performance and reliability) for you high-output n/a if you can swing the price upfront.

 

I have to agree on paper the 8 rotors look better.. but have to fall back on the results... people are getting no more performance than with the 89+ vintage N/A rotors..
Also you have to machine em for the 2MM seals that are deeper from the 89+ vintage motors.. plus "cobble" together miscellaneous parts from the 8 Kit and the 7 kit to make them work.... and you dont get any additional performance.

On my EP engine I decided to go with the 91 rotors I have VS the 8 rotors.. Less hassle.. same performance..
Also I am getting them lightened and balanced... soo it may all end up similar in the end.. (Weight wise)

 

I'd suggest either staying with 89-91 rotors or buying a complete renesis. This mix and match wrk seems a little too severe.

-Trent

 

That's the main problem I've ran into also with the rx-8 rotors. Supposedly someone is looking into the matter at Mazda Comp. They are aware of that particular problem. It seems the excessive clearance works well in the super heated enviroment in which they operate on the side port motors.
I also tried to lighten a rotor but the results were not very good. According to my machine shop they broke through the rotor with very minimum material milled off the sides. According to them it's not worth doing. I'm still waiting for the rotors to return to the shop so I can see the results.
Everyone above who are not getting positive results horsepower wise, most likely are due to side seal clearance. When you're dealing with NA motors compression is very important to acheiving good power.
I hope someone can come up with a solution quickly.

 

How much lighter are they again?

Once you modify them for deeper seals they can't be THAT much cheaper.

Is 9.7:1 vs 10:1 really going to be noticeable on most engines?

 

hmm. i hadent heard about the sealing and compression problems.

however i do remeber reading a thread about a guy who built a p-port race engine and got about 10% more power using reni rotors over s5 in an otherwise identical setup.

you cant argue that more compression isnt good for power, but i geuss if they cant seal well, a lightened s5 assembly will work well also.

 

The RX-8 rotors that i have were about 100 grams lighter than S5 which were 4360 grams. I think you can remove about 200 grams of the RX-8 rotors if you press out the rotor bearing and make 3 deep 360 degrees grooves in the bearig land. But you have to secure the bearing with lock screws becausse of the less contact surface.

 

Oh my god, you are planning on spending at least $2000-2500 just for rotors and rotating assembly in order to produce almost as much horsepower as a stock v8. Not to mention only last around 20k miles if that. I know that's a light car and all but still

 

show me where the v8 is as light and can be placed futher back into the fire wall

im trying to build a ca that is 1600lb.

and the engine will be were my money goes

race bearings
rx8 rotors
racing beat aluminum rotor housings
miata 6-speed

 

Now thats just silly..
20K is really inaccurate.. and I dont think this is the thread for this discussion.. but Dayum.. I have a couple V8 THings here at my house..
And Yes Torque.. But Umm.. They are novelties.. like a Pinto with a V8.

My main investment/fun is my 86 Sport that I am now done porting, and now looking at my clutch choices.

It is a preference thing.. but 20K is just plain incorrect.. unless the person is LOST when building it.. 250HP should last the life of a normal rotary if treated well. (As in 150K or so)

 

it will last more than 125k miles because at siguel racing there is a fb that has a j-ported 12a with the 51 adi and it has 120k miles on it .

 

Well fist of all if you use carbon seals needed for hi-revving bridge/j-bridge motors they don't last much longer than 20k or so. Secondly i hardly believe that any j-bridge port would last anywhere close to 30k even with steel apex seals as the water would get into the combustion chamber eventually, even on a very good built motor.

Now, if rotors is the way you want to go...just think of this, if you plan on spending so much money on your setup, wouldn't you be better off just putting a stock 13b rew and make more power, last longer, spend less money, not be as ridiculously loud, eat less gas, have a lot more bottom end...etc...Just a suggestion.

 

Spin racing, i noticed in your signature an LS1 rx7, now that thing would probably blow the doors off any n/a rotary or even a turbo one with just few mods, i'm not even talking about if you had a forced induction on it. And for what, the same money.

 

Yes you see the ? after it too. I have a 327 I have for it that was the original motor I was going to throw FI on and be in the 500 range. However it is going to be cheaper to just drop the LS1 and 6 speed in it.

It is still a novelty thing. Yes the all aluminum block and heads is all well and good.. and Yes it will be light etc. But it is still a novelty car.

Cant race it in SCCA.. cant Drag Race.. Cant really do anything but Autocross.. or do Track events.. (Not actually Race) Because you change the engine you are no longer legal for any racing.. Sooo Novelty. And the HP per cube isnt there either.

Far as blowing the doors off n/a or Turbo rotaries.. well.. No. I am sure there are quite a few people who could tell you the performance of thier rotaries that will beat out a somewhat modded LS1 RX. Mine will be a Daily driver. /shrug
Also they have 325HP... with alllllll the bolt on mods you are in the high 300s.. give it a 100 dry shot and you are at like 425-435..... soooo All the people I know with FDs have 450ish HP. How will the 325 beat out 450+???? a FC weighs a bit less.. but not that much of a difference.. Even throwing "NAWZ" at it.. you are still not that far behind a properly set up rotary.
Want to throw the wallet at them.. both end up in similar HP ranges.. soo its kinda moot.

 

I'm sorry i didn't mean to mess up the original guys post, i'm not going to argue the old v8 vs. rota argument (well that and also that an ls1 can barelly make only 425 hp on juice???). I was just surfing through and saw how much money people are willing to waste for miserable power, while popping apex seals in search for it...hey to each is own i guess.

Just some food for thought though (i just want to see what kind of an excuse anyone is going to come up for this one)...if rotaries are so great then how come they still haven't brocken the 6 second barrier in the 1/4 while 4 cylinders have been there for so many years now? Does that mean a cheesy 4 cylinder can actually pump out more HP, plus considering they are so much heavier? Just something i've always questioned when i used to be a rotorhead.

 

"if rotaries are so great then how come they still haven't brocken the 6 second barrier in the 1/4 while 4 cylinders have been there for so many years now?"

https://www.rx7club.com/rotary-car-performance-77/aussie-rotor-runs-6-99%40201mph-316609/

can you read up on rotaries a little bit before spouting crap.

 

its an n/a race car so...

 

boob
Abel Ibarra new drag car ( RX8 ) : 6.84 !!!! ......ONLY !

 

two or three rotors?

 

I'm sorry that only happened like a month ago...shame on me. It took so many years for the mighty 3 rotor to do what a 4 cylinder has been doing for at least 7 years.

 

umm...so.it has been done,and thats all that matters.youre just trying to spark another argument(of who got to 6-second 1/4 times??).you said...

i was just correcting your ignorant comment.and did i succeed?i think i did.so be definitely sure about the "facts" you post on this forum.